I'm noy a cryptography expert. Barely able to initiate a google
search -- it yields that the M.T. is not considered suitable for
cryptographic purposes.
So if our version is modified, or there are other reasons which
make it suitable as arc4random() replacement, it should
be documented, to appease such concerns.

It's just as "suitable" as arc4random(). We don't actually have
a cryptographically strong PRNG in the kernel. Both fail FIPS-140